Purification of phenanthrene by azeotropic distillation



March 25, 1952 J. FELDMAN ET AL 2,590,096

PURIFICATION OF PHENANTHRENE BY AZEOTROPIC DISTILLATION Fil'ed March 14, 1951 9 5 co 5 E L'- E U C Q) 1: CL 2 9 M Q (D O O O 1:0I IN IN N l r (\J m INVENTORS Milton Orchin ion Feld o v BY ATTORNE Patented Mar. 25, 1952 .UNITED r STATES PATENT PURIFICATION OF PHENANTHREN E BY AZEOTROPIC DISTILLATION Julian relaman and Milton Orchin, Pittsburgh, Pa.

OFFICE (Granted under the act of March 3, 1883, as

The invention herein. described and claimed may be manufactured and Government of the United States of America for out the payment of royalties thereon or therefor.

This invention relates to a method for sepaphenanthrene, fluorene, and carbazole by azeotropic distillation employing se- The invention is particularly governmental purposes with rating mixtures of lective entrainers.

phenanthrene contaminated fluorene, or both; an entrainer from the group amended April 30, 1928; 3700. G. 757) consisting of diethylene glycol, triethylene glycol, tripropylene glycol, tetradecanol, and heptadecan01, and distilling the resultant mixture within a range of subatmospheric pressures such that, in the course of the distillation, fluorene is removed in an overhead distillate, leaving behind the bulk of the phenanthrene, free from fluorene, While phenanthrene is recovered as an azeotrope with the entrainer substantially free from both used by or for the concerned with the purification of commercial I fluorene and carbazole, while carbazole which phenanthrene oils by the removal of relatively does not azeotrope is left behind as still bottoms. small amounts of fluorene and,carbazole there- The separations possible in accordance with from, with which these oils are usually conthe invention are based upon the discovery of taminated. the unique azeotropic behavior at varying dis- Phenanthrene is found principally as a relatillation pressures of this group of entrainers in tively large fraction in the distillation of coal tar, respect to the compounds involved. With the phenanthrene fraction usually representing phenanthrene, these entrainers form azeotropes about 4% of the total coal tar distillate. As obwithin a relatively wide range of subatmospheric tained from coal tar, phenanthrene is invariably pressures, in which the concentration of phenancontaminated with other polynuclear compounds, threne increases with decreasing distillation presparticularly anthracene, carbazole, and fluorene. sure. In the so-called commercial phenanthrene oil, With fluorene, these entrainers either do not there is ordinarily from 4% to 15% of anthraform azeotropes at all at atmospheric pressure cene, from 1% to 10% of carbazole, and from 1% or below, or else begin to form azeotropes at presto 10% of fluorene, and small amounts of other sures substantially higher than the distillation undetermined substances. Because of their relapressures at which phenanthrene azeotrope fortively small concentration, separation of these mation begins. With carbazole, these entrainers contaminants from phenanthrene by direct fraceither do not azeotrope at all, or form azeotropes tionation is not practical, and consequently they at pressures substantially lower than the distillahave generally been removed by other methods tion pressures at which phenanthrene azeotrope such as by solvent extraction and by chemical formation begins. techniques. These methods, besides being tedious By virtue of these relationships it is possible and expensive, tend to leave significant quantities to choose a subatmospheric distillation pressure, of impurities, particularly fluorene and carbazole or a series of decreasing subatmospheric distillain the phenanthrene. T tion pressures, such that during the course of the The principal object of the invention is to prodistillation the entrainer employed will form an vide a relatively easy and economical method, azeotrope or a eotrope with phenanthrene but involving azeotropic distillation with selective ennone with carbazole. D pending p n the ntrainers, by which fluorene and carbazole may be trainer selected, fluorene may or may not form removed quantitatively from admixture with 40 azeotropes with the entrainer within the range of phenanthrene. Other objects and advantages of distil a ion pr s r s mp y the invention will be apparent from the descrip- Fluorene, or the fluorene azeotrope, as the tion which follows. case may be, being the most volatile component Generally speaking, the objects of the invenin the system, is removed first in an overhead tion are accomplished by adding to impure distillate consisting of entrainer together with with carbazole, or fluorene and ordinarily small amounts of phenanthrene, leaving behind the bulk of the phenanthrene and all the carbazole. The loss of phenanthrene during the removal of the fluorene will depend upon the concentration of phenanthrene in the phenanthrene azeotrope formed at the particular distillation pressure or pressures employed. The more dilute the phenanthrene azeotrope, the smaller the carry-over of phenanthrene into the fluorene fraction.

The carbazole-phenanthrene-entrainer mixture, remaining after the removal of the fluo rene, is further distilled at subatmospheric pressures such that the entrainer azeotropes with phenanthrene but not with carbazole. The phenanthrene azeotrope distills oif leaving the carbazole behind as still bottoms.

The optimum distillation pressure or pressures to be employed will depend upon the particular entrainer selected and upon various economic factors. Relatively low distillation pressures between and 400 mm. Hg are to be preferred since the higher distillation temperatures required at distillation pressures above this range lead to rather rapid thermal deterioration of the entrainers'.

Since the phenanthrene azeotropes become more concentrated as the distillation pressure decreases, thus permitting the phenanthrene to be separated more rapidly from the carbazole, from this point of view, the lower distillation pressures are preferable. On the other hand, since the carry-over of phenanthrene into the fluorene fraction during the removal of the fiuorene increases as the phenanthrene azeotropes become more concentrated, from this point of view, higher distillation pressures are desirable. The optimum distillation pressure, or range of pressures, which balances these, and other factors in the most favorable manner must be determined in each case by consideration of all the costs involved.

In order to take full advantage of the change in the concentration of phenanthrene in the phenanthrene azeotrope as the distillation pressure changes, it will be in some cases desirable to conduct the separations at a series of different subatmospheric pressures, rather than at a single pressure. Thus, during the removal of at least part of the fluorene, the distillation pressure may be maintained in a relatively high range to minimize the carry-over of phenanthrene into the fluorene fraction. During the separation of the phenanthrene azeotrope from the carbazole, on the other hand, the distillation pressure may be decreased to a lower range to increase the concentration of phenanthrene in the azeotrope, thus to assist in more rapid separation of the phenanthrene from the carbazole.

The distillations may be conducted in accordance with a batch procedure or continuously as desired. For large scale separations continuous methods are, of course, more desirable.

Separation of the hydrocarbons from the entrainer after the distillation has been completed may be accomplished by any desired method. When the entrainer is water soluble, as is the case with diethylene glycol, triethylene glycol and tripropylene glycol, the hydrocarbons, being water insoluble, may be precipitated out by the addition of water to the mixture of entrainer and hydrocarbon, and the precipitate recovered by filtration or centrifuging. The water solution of entrainer thus produced may then be distilled, preferably at subatmospheric pressure, to strip off the water and recover the entrainer for reuse. Where the entrainer is water insoluble, as is the case with tetradecanol and heptadecanol, the. separation of the hydrocarbons from the entrainer may be accomplished by solvent extraction or similar methods, for example.

Of the entrainers listed above, diethylene glycol is particularly suitable and the invention will be described especially in reference to the use of this entrainer. While any of the entrainers in the group above give good results, diethylene glycol is relatively cheaper than the others. Likewise, being water soluble, it may be readily separated from the hydrocarbons and recovered for reuse. Since it is relatively low boiling, it produces relatively low boiling azeotropes with fiuorene and phenanthrene, thus permitting operation at relatively low temperatures at which diethylene glycol and the other components of the system are thermally stable.

With diethylene glycol, azeotrope formation with fiuorene begins in the neighborhood of atmospheric pressure, and fluorene azeotrope formation continues as the distillation pressure decreases to as low as 10 mm. Hg. With phenanthrene, azeotrope formation does not begin until a distillation pressure of about 400 mm. Hg is reached, and azeotropes of increasing concentration are formed as the distillation pressure decreases. In the table below the azeotrope composition (expressed in mole percent of phenanthrene) of phenanthrene-diethylene glycol azeotropes is given for various distillation pressures. This data was determined by distilling a sample of relatively pure phenanthrene in an excess of diethylene glycol at the distillation pressures listed- At each particular pressure, a small sample of distillate was collected at a high reflux ratio and analyzed.

TABLE 1 Concentration of Boiling Phenanthrene point of (in lnole per cent) A zeotropc in azcotrope 0.

Pressure mm. Hg

0. 10 220 0. 33 217 1. 02 20s 1. 49 l 196 2,30 180 s. 62 use 4. 34 146 In the ease of carbazole, on the other hand, no azeotrope formation with diethylene glycol occurs at distillation pressures above about 10 mm. Hg.

With the use of diethylene glycol, distillation pressures between 10 and 200 mm. Hg are preferable since efficient separations may be obtained in this range and at the same time, the entrainer is thermally stable at the temperatures required. In large scale separations, of course, a continuous procedure is preferable.

For a better understanding of the invention reference is now made to the drawing which schematically illustrates a continuous procedure for the purification of a raw phenanthrene oil by the removal of carbazole and fluorene therefrom in accordance with the methods of the invention. Rawphenanthrene oil, containing, for example, up to 10% each of fiuorene and carbazole, is introduced by line I into a mixing vessel 2 where it is mixed with an excess of the entrainer selected, preferably diethylene glycol.

The mixture of phenanthrene oil and entrainer is introduced continuously by line 3 into a distillation column 4 where fiuorene is removed as an overhead distillate by line 5. Distillation column 4 may be of any suitable type adapted for continuous distillation procedures such as the bubble-cap type, permitting the introduction of material at intermediate levels in the column. Preferably the mixture of impure phenanthrene and diethylene glycol or other entrainer is introduced into the lower portion of the column as shown.

Column 4 may be operated at any desired subatmospheric pressure at which the entrainer selected does not form an azeotrope with carbazole. Using diethylene glycol, for example, pressures ranging from about mm. to about 500 mm. Hg could be used. Preferably however this column is operated at relatively high subatmospheric pressures where relatively dilute phenanthrene azeotropes are formed, so that the fiuorene may be removed with a minimum loss of phenanthrene by carry-over into the fiuorene overhead. Using a diethylene glycol entrainer, for example, distillation pressures between 100 and 400 mm. Hg in column 4 would tend to minimize the amount of phenanthrene carried over during the removal of the fiuorene. Using diethylene glycol and operating column 4 at pressures in the neighborhood, of slightly greater than 400 mm. Hg, it is possible to recover fiuorene virtually free from phenanthrene since at pressures in excess of 400 mm. Hg phenanthrene does not azeotrope at all with diethylene glycol. This procedure has the disadvantage, however, that at the distillation temperatures required the entrainer would be somewhat unstable. With relatively high boiling entrainers such as tripropylene glycol and heptadecanol, the use of relatively high distillation pressures in column 4 is particularly desirable since these entrainers form relatively concentrated azeotropes with phenanthrene even at relatively high pressures.

From the bottom of column 4, the phenanthrene oil, from which fiuorene has been removed is withdrawn by line 6 and introduced into a second distillation column 'i. Column 1 is likewise a continuous type column and may be operated at any convenient pressure at which the entrainer selected forms an azeotrope with phenanthrene but not with carbazole. In this Way, the phenanthrene azeotrope may be distilled "off and removed as overhead, free from carbazole, by line 8, leaving carbazole as still bottoms. Preferably column I is maintained at a somewhat lower pressure than that prevailing in column 4 so that the azeotrope formed at this pressure will be relatively richer in phenanthrene than the phenanthrene azeotrope formed in column 4. Under these conditions, the phenanthrene azeotrope may be distilled off more rapidly and with use of less heat and a smaller quantity ofentrainer. In the case of diethylene glycol,

the pressure in the second column (column 1) is preferably maintained between 10 mm. and mm. Hg. Carbazole which does notazeotrope, is recovered free from both fiuorene and phenanthrene, from the bottom of column 7 by line 9.

The fiuorene, phenanthrene, and carbazole fractions are recovered from admixture with the entrainerby precipitation with water in vessels .nanthrene determined.

The following example illustrates the purification of a specific sample of a technical grade phenanthrene oil and shows the quantitative removal of both fiuorene and carbazole. The sample had the following analysis as determined by the countercurrent distribution method:

TABLE 2 Percent by Compound Determined Weight Phenanthrene Anthracene. Oarbazole Other impurities..- Unrecovered with the invention, the anthracene was first partially removed by formation of an adduct with maleic anhydride. A 589 gram sample of phenanthrene oil having the above analysis was re fiuxed with grams of maleic anhydride in a xylene solution for 15 hours. The xylene solution was then filtered, extracted with an aqueous alkali solution, and the xylene stripped away by distillation. This treatment removes the bulk of the anthracene leaving a residue of 553 grams of the original 589 gram sample. It is probable that some carbazole also was removed by this treatment.

The 558 gram residue was then distilled with 2 liters of glycol from a 5 liter pot through a Podbielniak column 3 feet tall and 1 inch diameter having 20 theoretical plates under the prevailing distillation conditions. During the distillation additional quantities of diethylene glycol totaling in all about 8000 ml. were periodically added. The distillation was conducted for a short time at a pressure of 216 mm. Hg. The pressure was then dropped to 100 mm. Hg, and distillation continued at this pressure until the fiuorene was completely removed from the distilland as an overhead azeotrope with diethylene glycol. The distillation pressure was then dropped to 20 mm. Hg and distillation at this pressure was continued until the phenanthrene was completely removed from the still as an overhead distillate, leaving carbazole as still residue quantitatively free from fiuorene and phenanthrene.

During the distillation, separate fractions of thedistillate were collected periodically. These samples were analyzed for percent hydrocarbon. After the fiuorene had been completely removed, the freezing point of the distillate was determined, and the mole percent purity of pheaseopee oess to the removal of fluorene only from a mix-- ture containing fluorene, phenanthrene, and

TABLE 3 [Azcoii'opic distillation l Volume Pressure Tempmm :A' Fraction Number in mi 1n mm. s

1 1 Weight -;1- M1 7.1 260 as 51 260 201 4.5 vs 260 211 4.0 212.6 100 1 173 12.8 382.1 100 I 178 13.7 2 .4.2 113 1 211 49.1 20 143 4.0 626 20 11 48 927 1 2o 1 14s 73 1.180 20 l 147 1 s7 1 2,286 a 2n 1 11s 9 1m 1 1 1175 l 20 i 115 1 so 881 1 2:1 14s 1 32 79:; Ls 2o 1 14 147 l 20 11.5 t I Total 8,810 .1 ..1

l Fluorenc and carbazolc Principally carbozolc.

It will be noted that during the distillation at 260 mm. and 100 mm. Hg the total overhead distillate collected amounted to only 7.4% of the original crude phenanthrene sample. Since this fraction includes all the iluorcne in the original sample, it can be seen that only slight losses of phenanthrene (3%-6%) are entailed in the quantitative removal of the iluorene.

The phenanthrene was recovered qauntitatively' free from fluorene and carbazole. The small amount of impurities remaining in the phenanthrene consist chiefiy of anthracene not removed by the maleic anhydride treatment. Anthracene is relatively easier to remove from phenanthrene than either fiuorene or carbazole by chemical methods and recrystallization, and if desired, substantially pure phenanthrene may beobtained by removal of this residual anthracene. The best sample (fraction 11) obtained by this distillation had a freezing point of 99.45" C and contained 0.86% anthr cene. The carbazole remaining in the still pot was quantitatively free from both fluorene and phenanthrene.

Hydrocabron Content Anthraccnc Content Freezing Mole-Percent Weight Curnu- Purity of Percent lativc Percent g {sli Phenanthrcnc I 0[ Weight Fraction Original Percent While the invention has been described par-.

ticularly in reference to the use of diethylene glycol as the entrainer, the other entrainers in thegroup. listed above behave in a fashion parallelto the behavior of diethylene glycol. In each case, by distilling at sub-atmospheric pressures, the fluorene is removed first as an overhead dis tillate leaving behind the bull: of the phenanthrene. The phenanthrene is invariably removed asan azeotrope with the entrainer eaving behind carbazole as still residue. The optimum range of distillation pressures varies somewhat of course with each entrainer. With triethylene glycol for instance, azeotrope formation with phenanthrene begins at relatively high pressures giving relatively concentrated azeotropes. At 500 mm. Hg, for example, phenanthrene forms an azeotrope with triethylene glycol containing over 30' mole percent phenanthrene. In such a case, during the removal of fluorene, the distillation pressure should be kept as high as practical to minimize the carry-over of fluorene in the overhead.

It is obvious,.of course, that the methods of l .08 0S 6. 3 82 S. 8 73 l. (33 5. l 2. 34 3. 97 (1. 0 3. 42 7. 39 4. 9 l. 75 12. 14 10. 6

. 73 12. S7 8. 15 S. 77 21. 64 7. 6'7 13. 3-5 34. 99 7. 88 15. 9O 50. S9 7. 37 29. 45 80. 34 7. 04 9. 14 89. 48 13 5. 8-6 95. 34 3. 63 2. 56 97. 90 l. 76 l Z. 10 100.00 7. 8

substances other than fluorenc and curbazole. and plionanthrcnc 00.0%.

carbazole, if this were desired, or to the removal of fiuorene from a mixture containing fluorene and phenanthrene but no carbazole. It is equally obvious that the methods of the invention could be employed to remove carbazole from a mixture containing phenanthrene and carbascle but no fluorene.

it is not necessary to use the entrainers listed above as the pure compound. Commercial mixtures sold under the name of the pure compound are generally suitable and are usually cheaper than the pure compound. For example, diethylene glycol is ordinarily sold as a mixture boiling between about 230 and 270 C. Triethylene glycol is usually sold as a mixture boiling between 270 and 300 C. Tetradecanol is ordinarily sold as a mixture boiling between about 255 to 270 C., while heptadecanol is available as a mixture boiling between 295 and 325 C.

The relatively pure phenanthrene obtainable in accordance with the invention will find many uses in paints, fungicides, insecticides, pyrotechnics, drugs, and dyes. It may be used, for example, to produce phenanthraquinone, a dye intermediate or may be oxidized to diphenic acid which is valuable for the production of a fiberforming resin.

Phenanthrene is, next to naphthalene, the most abundant single product of the coal tar distillate. By means of the present invention, this relatively abundant chemical is provided in a relatively pure condition by a cheap, easy method which is adapted to large scale continuous purification.

The carbazole which is produced as a byproduct of the purification is likewise relatively pure, being quantitatively free from both fiuorene and phenanthrene. Carbazole has valuable uses in the dye and pharmaceutical industry.

it is to be understood that the above description, together with the specific examples and embodiments described, is intended merely to illustrate the invention, and that the invention is not to be limited thereto, nor in any way ex-' cept by the scope of the appended claims.

We claim:

i. A-method for the purification of ph'enan'-- threne by the removal of fiuorene and-carba'z'ole' from admixture therewith comprising the steps of distilling the impure phenanthrene at subatmospheric pressures in the presence of an entrainer selected from the group consisting of diethylene glycol, triethylene glycol, tripropylene glycol, tetradecanol and heptadecanol.

2. The method in accordance with claim 1 in which the entrainer is comprised essentially of diethylene glycol.

3. A method for the purification of phenanthrene by the removal of fiuorene and carbazole from admixture therewith comprising the steps of adding to the impure phenanthrene an entrainer selected from the group consisting of diethylene glycol, triethylene glycol, tripropylene glycol, tetradecanol, and heptadecanol, and disstilling the resultant mixture within a range of subatmospheric pressures such that, in the course of said distillation, fiuorene is removed as an overhead distillate leaving behind the bulk of the phenanthrene, while phenanthrene is recovered as an azeotrope with said entrainer substantially free from fluorene and carbazole, leaving behind carbazole as still bottoms.

4. A method in accordance with claim 3 in which the entrainer is comprised essentially of diethylene glycol.

5. A method for the purification of phenanthrene by the removal of fluorene from admixture therewith comprising the steps of adding to the impure phenanthrene an entrainer selected from the group consisting of diethylene glycol, triethylene glycol, tripropylene glycol, tetradecanol, and heptadecanol, and distilling the resultant mixturewithin' a range of subatmospheric pressures such that, in the course of said distillation, fiuorene is removed as an overhead distillate leaving behind the bulk of the phenanthrene, uncontaminated with fiuorene.

6. A method in accordance with claim 5 in which the entrainer is comprised essentially of diethylene glycol.

7. A method for the purification of phenanthrene by the removal of carbazole therefrom comprising the steps of adding to the impure phenanthrene an entrainer selected from the group consisting of diethylene glycol, triethylene glycol, tripropylene glycol, tetradecanol, and heptadecanol, distilling the resultant mixture within a range of subatmospheric pressures such that, in the course of said distillation, said entrainer forms an azeotrope with phenanthrene, but not with carbazole, and recovering said phenanthrene as an azeotrope with said entrainer, leaving behind carbazole as still bottoms.

8. A method in accordance with claim 7 wherein said entrainer is comprised essentially of diethylene glycol.

9. A method for the purification of phenanthrene by the removal of fiuorene and carbazole from admixture therewith comprising the steps of adding to the impure phenanthrene an entrainer comprising diethylene glycol, subjecting the resultant mixture to a first distillation at a subatmospheric pressure such that said entrainer forms an azeotrope with fiuorene, and a relatively dilute azeotrope with phenanthrene, removing said azeotrope of entrainer with fluorene as an overhead distillate whereby the still bottoms become depleted of fiuorene, subjecting said still bottoms to a second distillation at a subatmospheric pressure lower than the pressure under which said first distillation was conducted and such that said entrainer forms a relatively concentrated azeotrope with phenanthrene but none with carbazole, and recovering said phenanthrene azeotrope as an overhead distillate, leaving carbazole as still bottoms.

10. A method in accordance with claim 9 in which the first distillation is conducted at pressures of from to 400 mm. of mercury, and in which said second distillation is conducted at pressures of from 10 to 100 mm. of mercury.

JULIAN FELDMAN. MILTON ORCHIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,892,770 Jaeger et a1 Jan. 3, 1933 1,892,771 Jaeger et a1 Jan. 3, 1933 1,892,772 Jaeger et al Jan. 3, 1933 2,358,128 Lake Sept. 12, 1944 2,358,129 Lake Sept. 12, 194% 

1. A METHOD FOR THE PURIFICATION OF PHENANTHRENE BY THE REMOVAL OF FLUORENE AND CARBAZOLE FROM ADMIXTURE THEREWITH COMPRISING THE STEPS OF DISTILLING THE IMPURE PHENANTHRENE AT SUBATMOSPHERIC PRESSURES IN THE PRESENCE OF AN ENTRAINER SELECTED FROM THE GROUP CONSISTING OF 